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Question
The product of the downstream and upstream speeds of a boat in a river is 8. What is the difference between the squares of the speed of the boat in still water and the speed of the stream?
A
8.
B
10.
C
12.
D
16.
Soln.
Ans: a
Ans: a
Let the speed of the boat in still water be u, and let v be the speed of the stream. The product of the upstream and downstream speeds of the boat is $(u + v) × (u - v)$, which is $u^2 - v^2$, and, therefore, the required answer = 8.